From: Nikunj A. Dadhania <nikunj@xxxxxxxxxxxxxxxxxx>
Certain architectures (viz. x86, arm, s390) have hardware page-table
walkers (#PF). So during the RCU page-table teardown process make sure
we do a tlb flush of page-table pages on all relevant CPUs to
synchronize against hardware walkers, and then free the pages.
Moreover, the (mm_users < 2) condition does not hold good for the above
architectures, as the hardware engine is one of the user.
This patch should also make the generic RCU page-table freeing code
suitable for s390 again since it fixes the issues raised in
cd94154cc6a ("[S390] fix tlb flushing for page table pages").
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Suggested-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Nikunj A. Dadhania <nikunj@xxxxxxxxxxxxxxxxxx>
[ Edited Kconfig bit ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
arch/Kconfig | 13 +++++++++++++
mm/memory.c | 23 +++++++++++++++++++++--
2 files changed, 34 insertions(+), 2 deletions(-)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -231,6 +231,19 @@ config HAVE_ARCH_MUTEX_CPU_RELAX
config HAVE_RCU_TABLE_FREE
bool
+config HAVE_HW_PAGE_TABLE_WALKS
+ def_bool y
+ depends on HAVE_RCU_TABLE_FREE && !(SPARC64 || PPC)
+ help
+ An arch should be excluded if it doesn't have hardware page-table
+ walkers that can (re)populate TLB caches concurrently with us
+ tearing down page-tables.
+
+ Both SPARC and PPC are excluded because they have 'external'
+ hash-table based MMUs which are cleared before we take down the
+ linux page-table structure. Therefore we don't need to emit
+ hardware TLB flush instructions before freeing page-table pages.
+
config ARCH_HAVE_NMI_SAFE_CMPXCHG
bool
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -329,11 +329,26 @@ static void tlb_remove_table_rcu(struct
free_page((unsigned long)batch);
}
+#ifdef CONFIG_HAVE_HW_PAGE_TABLE_WALKS
+/*
+ * Some architectures (x86, arm, s390) can walk the page tables when
+ * the page-table tear down might be happening. So make sure we flush
+ * the TLBs before freeing the page-table pages.
+ */
+static inline void tlb_table_flush_mmu(struct mmu_gather *tlb)
+{
+ tlb_flush_mmu(tlb);
+}
+#else
+static inline void tlb_table_flush_mmu(struct mmu_gather *tlb) { }
+#endif /* CONFIG_HAVE_HW_PAGE_TABLE_WALKS */
+
void tlb_table_flush(struct mmu_gather *tlb)
{
struct mmu_table_batch **batch = &tlb->batch;
if (*batch) {
+ tlb_table_flush_mmu(tlb);
call_rcu_sched(&(*batch)->rcu, tlb_remove_table_rcu);
*batch = NULL;
}
@@ -345,18 +360,22 @@ void tlb_remove_table(struct mmu_gather
tlb->need_flush = 1;
+#ifndef CONFIG_HAVE_HW_PAGE_TABLE_WALKS
/*
- * When there's less then two users of this mm there cannot be a
- * concurrent page-table walk.
+ * When there's less then two users of this mm there cannot be
+ * a concurrent page-table walk for architectures that do not
+ * have hardware page-table walkers.
*/
if (atomic_read(&tlb->mm->mm_users) < 2) {
__tlb_remove_table(table);
return;
}
+#endif
if (*batch == NULL) {
*batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
if (*batch == NULL) {
+ tlb_table_flush_mmu(tlb);
tlb_remove_table_one(table);
return;
}
--
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